RFR: 8321123: [Shenandoah/JDK21] Fix repo permissions [v3]

[Roman Kennke]

On Thu, 30 Nov 2023 17:48:21 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> The Shenandoah/JDK21u repo has the wrong permissons: it inherits permissions from jdk-updates, but should use permission from she Shenandoah project instead.
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Allow committers to review

Thanks!

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PR Comment: https://git.openjdk.org/shenandoah-jdk21u/pull/3#issuecomment-1834280070